Near Infrared Spectroscopy (NIRS) is a method that provides multi-constituent analysis of a variety of matrices. Recently, NIRS has gained wide acceptance within many industries for raw material testing, product quality control, and process monitoring. Within the agricultural community, NIRS has wide use both in research (measuring quality parameters of individual plants or plats), and in quality control and measurement of many commodities.
The NIRS region of the electromagnetic spectrum is defined as the wavelength range of 780-2526 nm, which corresponds to the wave number range from 12820-3959 per cm. The most prominent absorption bands occurring in the NIRS region are related to overtones and combinations of fundamental vibrations of —CH, —NH, —OH (and —SH) functional groups. NIRS absorption bands are typically broad, overlapping, and 10-100 times weaker than their corresponding fundamental mid-IR absorption bands. These characteristics restrict sensitivity and require chemometric data processing to relate spectral information to sample properties. The low absorption coefficient, however, permits high penetration depth. With such broad, overlapping peaks, the spectra are very complex. It is often difficult to assign specific features of the spectrum to a specific chemical. Therefore, sophisticated software, using multivariate calibration techniques, is required. A calibration equation must be developed using careful sampling, analyzing in the best traditional method, and application of multivariate calibration techniques.
NIRS has previously been utilized to measure the composition of the guayule plant, particularly the rubber and resin concentrations. The guayule plant is well known as a producer of latex or rubber. Previously, rubber and resin concentrations in guayule were measured by slowly and carefully grinding portions of the plant into a very uniform substrate. This uniform substrate, often difficult to achieve, was then analyzed with NIRS focused on one or two individual wavelengths, rather than the entire NIR spectrum. Another previous NIRS-based measured of guayule required the guayule to be dried and finely ground.